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Development and Growth Regulation

Photosynthetic Gas Exchange Characteristics of Wheat Flag Leaf Blades and Sheaths during Grain Filling

The Case of a Spring Crop Grown under Mediterranean Climate Conditions

Departament de Biologia Vegetal, Facultat de Biologia, Universitat de Barcelona, Diagonal 645, Barcelona 08028, Spain

The rate of net CO₂ assimilation (A), the stomatal (g_s) and residual (g_r) conductances to CO₂, the intercellular CO₂ concentration, the CO₂ compensation points at 21% O₂ (₂₁) and at 2% O₂ (₂), and the amounts of dry matter, nitrogen, and carbohydrates were determined, from anthesis through grain filling, in the flag leaf blade and sheath of spring wheat (Triticum aestivum L. cv Kolibri). The nitrogen content and the rate of net CO₂ assimilation declined slowly until the onset of senescence in both organs, about 3 weeks after anthesis. During senescence the reduction of A in both organs was not primarily caused by a decrease in g_s; the main factor is the decrease in g_r. From values of ₂₁ and ₂ it is suggested that the rate of respiration in the light contributing to the CO₂ compensation point is higher in sheaths than in blades irrespective of the O₂ level considered. The role of sheaths storing and later transporting assimilates to the developing grains seems to be more important for shoot yield than that of sheaths functioning as photosynthetic organs after the onset of senescence occurs. It is suggested that accumulation of carbohydrates in leaves might somehow trigger senescence in the flag leaf blade and sheath simultaneously.

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				J. Bertheloot, P. Martre, and B. Andrieu Dynamics of Light and Nitrogen Distribution during Grain Filling within Wheat Canopy Plant Physiology, November 1, 2008; 148(3): 1707 - 1720. [Abstract] [Full Text] [PDF]